Comparison of CH4 Flux Measurement by Open- and Close- Path Eddy Covariance System

doi:10.3969/j.issn.1000-6362.2019.11.001

Abstract

Abstract: The eddy covariance technique provides a useful tool to directly measure CH4 exchange between the vegetation and the atmosphere. The open-path (OPEC) and close-path (CPEC) systems have uncertainties in measuring methane flux in forests. Therefore, it is necessary to compare the measured CH4 flux obtained from the OPEC and CPEC systems. In this study, CH4 flux was measured using the OPEC and CPEC systems in a mixed plantation in the Xiaolangdi area during the growing season of 2016 (July 24th to August 5th). The (co)spectra were analyzed and the time lag was estimated. Moreover, CH4 flux from the OPEC and CPEC systems was discussed. The results showed that the (co)spectra showed a good agreement with the -5/3 for spectra and -4/3 for co-spectra. Under different sampling flow rate (40, 37.5, 35.5, 33.5 and 31.5L·min-1) conditions, the time lag was 4.6, 7.7, 5.3, 10.8 and14.3s, respectively, and the average lag time was 8-9 s. CH4 flux derived from the CPEC system was 12% lower than that measured by the OPEC system in sunny days, while CH4 flux obtained by the CPEC system was 32% higher than that measured by the OPEC in rainy days. The OPEC system was more suitable measuring CH4 flux in comparison with the CPEC system in sunny days. The lag time should be corrected for the CPEC system in rainy days since it can be used for compensate for missing values in the OPEC system. Higher quality data of CH4 flux can be obtained by using the CPEC and OPEC systems together.

Key words: Eddy covariance, Lag time, Spectrum analysis, Methane flux, Forest ecosystem

YUAN Wen-wen，ZHANG Jin-song，MENG Ping，TONG Xiao-juan，PAN Qing-mei，HE Fang-jie，LI Jian-xia. Comparison of CH4 Flux Measurement by Open- and Close- Path Eddy Covariance System[J]. Chinese Journal of Agrometeorology, 2019, 40(11): 669-677.

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